High-frequency multiplex signaling system



Oct. 6, 1925. 1,556,321 1. ESPENSCHIED HIGH FREQUENCY MULTIPLE SIGNALINGSYSTEM ginal Filed Sent. 30. 1919 ave "01 filfsp ensdlkd 3:51 abhor/14Patented e. 6,1925.

UNITED STATES PATENT OFFICE.

LLOYD nsrnascmn, 0F QUIIIS, NEW YORK, ASSIGHOB '1'0 AMERICAN TELEPHONELID TELEGRAPH column, A COBIOBATIOH OF NEW YORK.

mGH-FBEQUBIGY IULTIIILEX SIGITAIJNG SYSTEI.

(Mgiaal application fled September 80, 1919, Serial Io. 827,801. Dividedand this application fled April a, 1:21. Serial Io. mass.

To all whom it may concern:

Be it known that I, Lnoro Esrnuscnmo, residing at Queens, in the countyof Queens and State of New York. have invented cerl tain Improvements inHigh-Frequency Multiplex Signaling Systems, of which the fol lowing is aspecification.

This invention relates to high frequency multiplex signaling system andmore particularly to a terminal circuit arrangement embod the use ofamplifiers adapted to 'ampli the side band and the carrier frequencyoscillations received by the said terminal circuit. I

This application is a. division of my cogznding application, Serial No.327501 filed ptember 30, 1919, entitled High frequency multiplexsignaling system.

The broad object of the invention is to improve the transmissioneflicicncy and the transmission quality of carrier current circuits. Onefeature is the provision of a carrier current amplifier for improvingthe transmission efliciency of the carrier circuit.

35 A further object of the invention is to provide means whereby theratio of the unmodulated carrier current transmitted over the system tothe modulated or side band component may be controlled for the purposeof insuring good quality in the carrier transmission circuit.

A comprehensive understanding of the invention will be facilitated byrecognizing that in the ordinary form of carrier current transmissionrepresented by radio, there are involved really two channels, one theunmodulated carrier current which is transmitted over the system at theoriginal car rier frequency and the other the modulated or side handcomponent which is at a frequency differing from the original carrierfrequency by an amount corresponding to the signaling frequency. Thesetwo channels are commonly treated in radio, for example, as a singlechannel, and at the receiving end are fed unseparated into the detector.The detecting action obtains, however, only by virtue of modulationbetween, that is, the beating together of, the currents of the twochannels, the carrier and one or both side bands. The present inventionis concerned with carrier current systems, both wire and wirelem,wherein the carrier is transmitted directly along with the side bands asper ordinary radio practice, as distlngulshed from the type of carriersystem first employed for multiplex service over wires wherein thecarrier channel is suppressed at the sending end and resupplied at thereceiving end by .a control system.

One feature of the invention resides in the use of an am lifier in thehigh frequenc part of the circuit which amplifies simu taneously boththe carrier and the side band currents. A given amplification insertedin this manner in the hlgh frequency circuit results in a twofoldamplification of the detected current by virtue of the fact that theamplitude of the detected current is a function of the product of theamplitudes of th carrier and the side band currents.

It has been found that for the obtaining of good quality in carriertelephone transmission, it is necessary that the carrier supply currentbe large compared with the side band currents. This relation isnecessary in order that in detection or demodulation, the product termof carrier and side band, representing the desired detected current ofsignaling frequency, be large in amplitude compared with the otherproduct terms such as those resulting from modulation between the twoside bands or between the component currents of one side band, whichcurrents represent undesired detected currents tending to interfere withand depreciate the quality of the transmission. A further feature of theinvention is the provision of means whereby the carrier and the sidebands may be amplified in difierent proportions, that is, the ratio ofthe amplitudes of the to the side band currents may be varied for thepurpose of improving quality in the manner indicated. This isaccomplished by combining with the high frequency amplifying apparatus,selective circuits whi discriminate as between the carrier frequency andthe side band frequency.

The drawing shows the application of the invention to a terminal circuitof the type characterized by a single translating circuit adapted tomodulate and demod ate the outgoing and incoming currents. In the figureL represents the high frequency line over which it may be assumed thatcurrents of the frequency n and n-f are being received. Thesefrequencies are impressed by the transformer T upon the input circuit 1.

- the common conductor of the duplex modulating and demodulating deviceMD,. As. sociated with the high frequency output branch 2 is a highfrequency band filter F F and F represent low frequency filters whichare adapted to transmit currents of the signaling frequency. The mode ofoperation of this circuit is as follows: Let it be assumed that thecarrier frequency at and a band of frequencies represented by n-f, arebeing received over the line L from the circuit at the opposite end ofthe said line, and are being. impressed upon the receiving branch 1 ofthe terminal circuit shown in the figure. The band of frequenciesrepresented by n-f will pass through the filter F and will be impressedby the transformer T upon the modulating and demodulating device MD,.The carrier frequency at will be selectively amplified by the amplifierA and the amplified oscillations of this frequency will be impressedupon the translating device MD The low frequency signaling currentresulting from demodulation will be impressed by the transformer T uponthe output side of the terminal circuit and passing through the lowfrequency filter F will be impressed upon the low frequency signalingcircuit L The low frequency signalng currents set up in the circuit L bythe low frequency signaling apparatus associated therewith will beimpressed upon the input branch 4 of the transmitting path and p ssingthrough the low frequency filter F, will be impressed upon thetranslating circuit by the transformer T These low frequency currentswill modulate the amplified high frequency carrier current impres edupon the translating circuit by the amplifier A and the modulated highfrequency current resulting therefrom will be impressed upon the outputcircu t by the transformer T9. These modulated high freuencyoscillations will pass through the hi h frequency band filter F and overthe transmission line L,.

It will be seen therefore that by means of he arrangement shown in thefigure the unmodulated carrier oscillations which are simultaneouslytransmitted together with one or more of the side bands based upon thiscarrier frequency may be separated from the said band or hands in thereceiving branch of the terminal circuit and may be amplified separatelyfrom the side bands and impressed upon a translating circuit common tothe transmitting and receiving paths of the terminal circuits.

It will furthermore be seen that bysuitable adjustment of the amplifierA, the relative amplitudes of the carrier oscillations and the side handoscillations may be controlled. It will also be seen that by means ofthe balanced duplex translating circuit oscillations of the carrierfrequency are suppressed therein and do not pass through the transformerT Consequently this tends to reduce the possibility of singing in casethe balancing networks did not exactly bala'ncetheir corresponding linecircuits. Although this invention is disclosed as embodied in a wiresignaling circuit it is to be understood that it is equally applicableto radio transmission systems.

Furthermore, although this invention has been shown as embodied incertain specific formor arrangement of parts, it is to be understoodthat it may be embodied in other and differentforms and arrangementswithout departing from the spirit and scope of the appended claims.

What is claimed is: v

1. In a signaling system adapted for the transmission and reception ofhigh frequency signals, the method which consists in simultaneouslyreceiving from a common medium modulated high frequency oscillations andunmodulated high frequency oscillations, separating the two types ofoscillations, amplifying the unmodulated type, and detecting themodulated oscillations by means of the amplified unmodulatedoscillations.

2. In a signaling system adapted for the transmission and reception ofhigh frequency signals, the method for improving the quality ofdetection for signals which consists in simultaneously receiving from acommon medium modulated and unmodulated carrier currents, selectivelyseparating the said modulated and unmodulated currents, amplifying theunmodulated carrier current, to a definite degree, depending on theamplitude of the modulated current, and detecting the modulated currentby means of the amplified carrier current.

3. In a signaling system adapted for the transmission and reception ofhigh frequency signals, the method for improving the quality ofdetection of signals which consists in simultaneously receiving from acommon medium modulated and unmodulated carrier currents, selectivelyseparating the said modulated and unmodulated currents, amplifying theunmodulated carrier current to a definite degree, depending upon theamplitude of the modulated current, detecting the signaling component ofthe modulated current by means of the amplified carrier current,suppressing the unmodulated carrier current and transmitting thedetected current.

.4. In a signaling system adapted for the transmission and reception ofhigh frequency signals, the method which consists in simultaneouslyreceiving low frequency signaling Variations and unmodulated highfrequency oscillations, amplifying the said oscillations, modulating theamplified oscillations by means of said variations, suppressing theunmodulated high frequency oscillations and transmitting the modulatedhigh frequency oscillations.

5. In a signaling system, the combination with two line" circuits one ofwhich has a source of unmodulated carrier current associated therewithof a four-wire connecting circuit having atranslating circuit associatedtherewith comprising means to modulate and demodulate impressedoscillations, filters arranged in the t'wo-wire branches of thefour-wire circuit so as to provide proper paths for the transmitted andreceived currents and a by-pass circuit connected with one of saidtwo-wire branches having a filter and an amplifier associated therewithadapted to select and amplify the unmodulated carrier current and meansto impress said amplified carrier current upon the said translatin gcircuit.

6. In a signaling system, a combination of two line circuits, one ofwhich has a source of carrier current associated therewith and afour-wire connecting circuit characterized by a translating circuitcommon to the transmitting and receiving paths of the four-wire circuitand having means to modulate and demodulate the currents flowing throughsaid transmitting and receiving paths, and further characterized bymeans to select and amplify the carrier frequency current beforeimpressing it upon the said translating circuit.

7-. In a signaling system, the combination of two line circuits, havingconnected therewith sources of low frequency and high frequency currentsrespectively and a four-wire 8. In a signaling system, the combinationof two line circuits each having sources of current connected theretoand having networks individual thereto adapted to balance said lines, afour-wire connecting circuit electrically related to said line circuitsby conjugate transformers, a translating circuit bridged across thetwo-wire branches of the four-wire circuit, common to the trans mittinand receiving paths of the fourwire clrcuit, low pass and high frequencyband filters in each of the said two-wire branches, and a by-passcircuit connecting one of said twofwire-branches and said translatingcircuit and having means to select and amplify currents from one of said"sources and to impress the amplified currents on said translatingcircuit.

9. In a high frequency signaling system,

the combination of a receiving circuit adapted for the reception ofoscillations of the side band frequencies and oscillations of thecarrier frequency, a detector, means for selectingand amplifyingoscillations of the carrier frequency to the exclusion of the side bandfrequencies and means for impressing simultaneously upon the saiddetector oscillations of the side band frequencies and amplifiedoscillations of the carrier frequency.

In testimony whereof, I have signed my name to this specification this7th day of April 1921.

LLOYD ESPENSCHIED.

